Roman Black wrote: > Hi, in messing around I came up with a *really simple* 2-tran boost > circuit that gives 13.3v regulated output from a regulated 5v input. > > It supplies up to 12mA @ 13.3v, but only starts up reliably when output > load is about 10k (about 1mA) during startup. Only 2x NPN tran, 1N4148 > and cheap rf choke, 4 resistors, 2 caps, 13v zener. > > It can be turned on/off at will by attaching one tran base to a PIC output. > > I think Myke was after something like this for a cheap PIC programmer > etc? If this spec is acceptable i'll write it up or does it need more > current etc?? Yes, please do. I'd like to see how it compares with one that I came up with a few days ago. I need a regulator that can take a battery voltage of 3-4 volts and provide 5V at up to 100 mA max with good efficiency. I came up with a circuit with 5 res, 2 cap, zener, choke, 1 NPN and 1 PNP. diode 3-4 V o----+------------CCCCC---+---AK----+---+----o 5V @ 100 mA | 68 uH | | |+ R +------+ R --- 100uF 1000 R | .001| R --- R PNP | --- R | | 100 C --- | V +--+---E C---RRRRR--B NPN | | Gnd | | B E +--+ LM336 Z --- | | | | -2.5 Z --- | V | R Z |.047| 2200 Gnd | R | V +---RRRRR-----------+ R V Gnd | Gnd V Gnd Actually, the two resistors providing the voltage divider for the feedback are a 25K pot on my breadboard. I'm not sure what it's actually set to. And the "zener" is actually an LM336, because I have a few on hand. The circuit starts up just fine under load, at least under modest loads of 15 and 30 mA. Load regulation seems really solid, but I'm not happy with the efficiency. The problem is the base drive of the switching transistor, which needs to be high enough for the peak coil current, but doesn't contribute to the output current at all. This is probably an application that really needs a FET instead of a BJT. I think I'm better off with a MAX1678, which achieves >80% at 1mA load current at 5V (!). I've ordered some samples. Anyway, Vpp supply would be a good application for this type of circuit. Let's see yours, then we can tweak from there. -- Dave Tweed -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.